There isn't any at the moment. All of them are having problems. If someone ever says to you "exchange A is great and nobody ever had any problems", he is lying.
Polo: Many withdrawal problems. Locked currencies, wallets...
Cex.io: Is in trouble with the FEDs
Btc-e: same
Kraken: same
Finex: Ticking bomb
Coinbase: Joking right?
It is time for us to push for decentralized exchanges. Oldschool exchanges has little time left.
What about Bitstamp? It offers not much currencies, only 3 and only BTC among requested by author, but anyway..
BitStamp doesnt offer Leverage trading. Its the only exchange who hasnt faced any problem other than its hack some years ago.